Seasonal Climate Outlook Message for September to December 2002

The bottom line

Mixed outlook Across Queensland (Dated 10/09/02)

The 30day average of the SOI as of the 10th of September is -13.1.

Despite the fall in the value of the SOI over August, the chance of above median rainfall for September to November is mixed across Queensland. For example the chance of above median rainfall over the next 3 months in parts of the central west is quite low (20-40%), yet across much of the western Darling Downs probabilities are more reasonable (40-60%).

An El Nino sea surface temperature pattern still exists in the Pacific Ocean.

The full story

Mixed Outlook Across Australia (Dated 10/09/02)

Based on the recent pattern of the SOI, the probability of getting above the long term median rainfall for September to November is mixed across most of Australia.

For example, in Queensland currently there is a 25% chance of getting above the long term September to November median rainfall of 65mm at Charters Towers. This compares with a 52% chance of getting above the long term September to November median rainfall of 155mm at Dalby. This mixed outlook may be reflecting some instability in the current El Nino pattern.

In NSW the probability of above median rainfall for September to November remains low (20-40%) for much of the central and eastern half of the state. However for parts of the western half of state probabilities are higher at 50-60%. A similar pattern also exists in Victoria and Tasmania.

Generally speaking, for the rest of Australia the probability of above median rainfall for September to November is relatively low. However this depends on the location.

As rainfall probabilities and median rainfall levels vary across the state, we recommend referring to Australian Rainman or contacting the DPI Call Centre on 13 25 23 for more specific rainfall data for your location.

As always when dealing with probabilities it is essential to consider the additional information that probabilities provide. For example based on the recent pattern of the SOI there is a 30% chance of getting above the long term September to November median rainfall of 76mm at Barcaldine. Therefore there is a 70% chance of not getting the long term September to November median rainfall.

Another way of looking at this is that in approximately one third of years (3 years out of 10) with the current SOI pattern, Barcaldine has received its long term median September to November rainfall. Therefore in around two thirds of years (7 years out of 10) with the current SOI pattern, below median rainfall has been recorded at Barcaldine for September to November.

The monthly value of the SOI for July was -7.1 and August was -14.3. Based on this shift in value over September to November the SOI is now in a "Rapidly Falling" phase.

For those readers who like to follow historical patterns more closely, years that have had a "Rapidly Falling" SOI phase in July/August include1997, 1991, 1989, 1986, 1979, 1957, 1953, 1936, 1934, 1921 and 1902. What where the farming and or rainfall conditions like for September to November in your area for those years? The internet site www.longpaddock.qld.gov.au has details on the rainfall received in those years.

The rainfall events that occurred across much of south and south east Queensland in late August coincided with the passage of the 30-50day intra-seasonal oscillation (also know as the MJO). Regular readers of this column would be aware of the usefulness of the MJO in helping to predict the timing of rainfall over Queensland.

The MJO is simply a band of low atmospheric pressure that originates off the east coast of central Africa. It travels eastward across the Indian Ocean and northern Australia roughly every 30 to 50 days. While it is mainly a tropical phenomenon, it appears to indicate the timing of potential rainfall events (but not indicate rainfall amounts) over central and southern Queensland by helping to enhance atmospheric activity such as upper level low pressure systems.

The use of the MJO as a reliable forecast tool is still at the research/experimental stage. The DPI and the Uni of Southern Queensland currently have a study project under way looking at the use of the MJO as reliable rainfall prediction tool for Queensland. It is next expected around late September/early October. Given current dry conditions, many producers will be waiting to see if the next passage of this phenomenon will help create some more relief rainfall.

Recent sea surface and sub-surface temperature data sourced from both the Climate Prediction Centre in the United States http://www.cpc.ncep.noaa.gov/ and the Bureau of Meteorology http://www.bom.gov.au/ highlight an 'El Nino' sea surface temperature pattern in the Niño 3 and 4 regions of the equatorial Pacific.

It is worth noting that each El Nino event is unique with respect to rainfall patterns and areas affected by dry conditions. The Bureau of Meteorology has an interesting site http://www.bom.gov.au/climate/ahead that provides a good summary of the rainfall patterns that have occurred in previous El Nino years.

An idea of how each El Nino is unique can be gained by comparing the impacts of each event. For example, during the 1987/88 El Nino event, mainly average to above average falls were recorded in Victoria, NSW and Queensland during the 9 months from May 1987 to January 1988. However for the north and east of Tasmania, pockets of the Gippsland and the south west corner of WA, rainfall totals for the 7 months from Apr-Oct 1987 were in the lowest 10% recorded. There was also a poor wet season over northern Queensland for the 6 months from Oct 1987 to March 1988.

In the 1991/92 El Nino event, about three-quarters of Queensland recorded rainfall totals for the 9 months from March to November 1991 in the lowest 10% of records. For much of the Darling Downs it was the driest such period on record. The northern half of NSW was also seriously affected during this period. Across northern Australia (WA, NT, north Qld) rainfall totals were also consistently below average from November 1991 through to April 1992.

However further south, rainfall totals were average to above average although the rainfall distribution during this period was very uneven.

Our strong advice as always remains to monthly monitor SOI trends and sea surface temperature patterns. As an El Nino event is occurring we encourage readers to consider what any repercussions and/or benefits an El Nino could mean to their businesses.

For more information try the DPI climate web site www.dpi.qld.gov.au/climate on which the 'Climate Note" can be found.